I haven't seen it in this colony, but I have in different colonies. I think a number of reefers believe that it's because of splitting, but I'm not entirely convinced that's the case. I have seen this in instances where the torch/hammer/frogspawn is no where near splitting as well. I've seen it just before a polyp bailout and I've seen it just before a split.
There's no scientific fact to this statement, but I'd tend to believe this is more likely a reaction to stress or an irritant (which could include stress from splitting as well). This bubbling is also a behavior you see sometimes in bubble tip anemones as well.
Hopefully, in your case, it is because the torch is splitting.